1. Field of the Invention
The present invention relates to insulated concrete, and, more particularly, to insulated concrete using a closed cell plastic foam insulation layer.
2. Description of the Related Art
It is known to insulate concrete driveways and walkways by placing a sheet of approximately one inch thick closed cell plastic foam, such as polystyrene or styrofoam (.TM.), between the ground and the concrete. The closed cell plastic foam insulates the concrete from the ground and inhibits the concrete from sweating. The pieces of closed cell plastic foam typically measure approximately 4 feet by 8 feet.
A problem associated with this method is that the pieces of closed cell plastic foam may break under the weight of the concrete or a worker during pouring of the concrete. This breakage typically results in multiple fracture lines running almost the entire length of the sheet, causing the whole board to be damaged or wasted.
Moreover, it is known to heat the concrete to melt and/or inhibit the accumulation of ice and snow thereon. A heater assembly may include a heater wire which is suspended in the layer of concrete using standoffs, reinforcing rod, etc. When using a conventional 4.times.8 sheet of closed cell plastic foam insulation, the worker first lays down the 4.times.8 sheet of closed cell plastic foam and then installs the standoffs, rebar and/or heater wire. Since the worker cannot reach to the center of the 4.times.8 sheets, it is usually necessary for the worker to walk on the 4.times.8 sheet to install the standoffs, rebar, heater wire, etc., thereby resulting in the above-mentioned breakage of the closed cell plastic foam insulation.
Another disadvantage associated with a worker walking on the closed cell plastic foam insulation is that the insulation is permanently compressed at the impact locations, thereby resulting in a decreased insulating or "R" value. If the concrete layer is heated, this decrease in the insulating value of the closed cell plastic foam insulation may result in additional loss of heat to the ground, thereby reducing the heating efficiency.
Breakage of the conventional 4.times.8 sheets of closed cell plastic foam insulation is further increased if the ground upon which the insulation is disposed is not perfectly flat. That is, the closed cell plastic foam insulation is a relatively brittle material when subjected to a loading force. If the 4.times.8 sheet of closed cell plastic foam insulation spans a depression or projection on the ground, it is possible that the weight of the concrete and/or worker will relatively easily break the sheet of insulation.
Another problem is that these large pieces of closed cell plastic foam do not conform well to curves. The closed cell plastic foam has to be cut into smaller pieces to completely cover the area within the boundaries of a curved driveway without the closed cell plastic foam extending beyond the boundaries of the driveway (FIG. 1). This may result in wastage of all of the closed cell plastic foam falling outside the driveway boundaries, as all of this extra closed cell plastic foam must be cut off.
What is needed in the art is a way to insulate a layer of concrete with closed cell plastic foam such that less closed cell plastic foam is wasted due to breakage under the weight of the concrete or a worker during pouring of the concrete, and less closed cell plastic foam is wasted due to being cut to conform to the boundaries of the curves of a driveway.